This research will be done primarily in Brazil at Federal University of Rio de Janeiro in collaboration with Ethan Bier as an extension of NIH grant # RO1 NS 29870. During dorso-ventral (DV) patterning of the Drosophila embryo, a series of maternally expressed genes define the initial subdivision of the axis into ventral mesoderm, lateral neuroectoderm and dorsal ectoderm. Ventral activation of the maternal Toll receptor signals for degradation of the Ird3 homologue Cactus through the ubiquitin pathway, releasing Dorsal, a transcription factor of the Rel/NFkB family, for nuclear translocation. This Dorsal nuclear gradient defines the extent and location of the three DV territories. We have shown that signaling by the TGF-B family member decapentaplegic (dpp), which is antagonized by the product of the short gastrulation (sog) gene, plays a role in creating the Dorsal gradient. Increased maternal Dpp signaling blocks Cactus degradation through a "signal independent" pathway, parallel to Toll signaling, shifting all DV gene expression domains ventrally. Although several elements of the Toll pathway have been described and are known to be highly conserved between vertebrates and invertebrates, the components of the signal independent pathway of Cactus degradation remain unknown. We propose to identify elements that connect the TGF-B and Toll pathways and to analyze the mechanism by which they function. Several lines of evidence indicate Calpain-dependent proteolysis of IkB as an alternative to processing through the proteosome. In addition, it has been shown in Drosophila that mothers double heterozygous for null alleles of dorsal and Calmodulin generate embryos with DV patterning defects. Therefore, maternal calcium signaling elements may regulate gene expression along the DV axis. We will investigate whether calcium-dependent processes bridge maternal Dpp signals for Cactus degradation. Considering the high degree of evolutionary conservation of the Ca +2 pathway it is likely that mechanisms by which these signaling networks link the TGF-B and Toll pathways in Drosophila will also have physiological relevance in vertebrates.